7.6 - Blood Vessels And Their Functions Flashcards
What are the three main blood vessels?
- veins
- capillaries
- arteries
What do arteries do?
Carry blood away from the heart and into arterioles
What do arterioles do?
They are smaller arteries that control blood flow from arteries to capillaries
What do capillaries do?
Link arterioles to veins
What does the tough fibrous outer layer do?
Resists pressure changes from both within and outside
What do veins do?
Carry blood from capillaries back to the heart
What does the muscle layer do?
Can contract and so control the flow of blood
What does the elastic layer do?
Helps maintain blood pressure by stretching and springing back (recoiling)
What is another name for the thin inner lining?
Endothelium
What does the endothelium do?
Its smooth so reduces friction and is thin so allows for diffusion
What is the lumen?
Its not a layer but is the central cavity of the blood vessel through which the blood flows
Why is the arteries muscle layer thicker compared to veins?
This is because the smaller arteries can be constricted and dilated in order to control the volume of blood passing through them
Why is the elastic layer in arteries relativly thicker compared to compared to veins
Because it is important that blood pressure in arteries is kept high if blood is to reach the extremities of the body.
How does the elastic lining keep the pressure up in the arteries?
The elastic wall is stretched at each beat of the heart. It then springs back when the heart relaxes in the same way as a stretched elastic band. This stretching and recoil action helps maintain high pressure and smooth pressure surges created by the beating of the heart.
Why are there no valves in arteries?
Because blood is under constant high pressure due to the heart pumping, it therefore tends to not flow backwards
Why is the mucle layer thicker in arterioles than in arteries?
The contraction of this layer allows constriction of the lumen, this restricts the flow of blood and so controls its movement into the capillaries that supply the tissues with blood
Why is the elastic layer thinner is arterioles that in arteries?
Because the blood pressure is lower
Why is the vein muscle layer relatively thin?
Because veins carry blood away from the tissues and therefore their constriction and dilation cannot control the flow of blood to the tissues.
Why is the elatic layer thin in veins?
Because the low pressure of blood within them wont cause them to burst and the pressure is to low to recreate a recoil action
Why is the overall thickness of the vein wall small?
Because there is now need for a think wall because the pressure within veins is too low to cause any risk of bursting, it also allows them to be flattened easily, aiding the blood flow within them
Why are there valves in veins?
To stop blood flowing backwards which it might do because the pressure is so low
How to veins create a blood flow?
When body muscles contract, veins are compressed, pressurising the blood within them, the valve ensure that this pressure directs the blood in one direction only - towards the heart
Why do capillary walls consist of mostly the lining layer?
Because it makes then extremely thin - making the diffusion distance shorter.
What makes the capillaries have a large surface area for gas exchange?
They are numerous and highly branched
